Studies from our laboratory have shown that phosphorylation of H1 histone increases across the cell cycle and is elevated twenty fold during G2 just prior to mitosis. Postmitotic G1 cells exhibit a rapid dephosphorylation. Based on these studies it has been postulated that phosphorylation of H1 histone is directly involved in hypercondensation of chromatin during the mitotic cell cycle. Currently we are assessing DNA, RNA and protein context, as well as BrdU incorporation to analyze cells and/or nuclei from cultures of synchronous and asynchronous cultures of human skin fibroblasts. Nuclei will be sorted for subsequent analysis of nucleoprotein content and composition. Correlation will be made of nucleoprotein phosphorylation profiles, cell cycle position and metabolic capacity of cells. The general protein kinase inhibitor, staurosporine, a drug we have shown at low levels arrests normal cells, but not transformed cells, in G1 phase, will be employed in these studies.